1. Field of the Invention
The present invention relates to a method for conducting crash tests using a carriage, in particular for simulating the collision of a motor vehicle with an obstacle, in which the deceleration forces of a real collision are simulated. The invention moreover relates to an apparatus for carrying out such a method.
2. Description of the Related Art
When a vehicle collides with a resistance, for example another vehicle, in an accident, it is decelerated in accordance with the deformability of each of the vehicle and the resistance (e.g., the other vehicle). This deceleration initiates an acceleration onto the movable masses of the vehicle. In order to be able to investigate these acceleration forces, it is known to conduct real crash tests in which a vehicle is accelerated to a desired speed and collides with an obstacle. The vehicle is, however, destroyed thereby and cannot be used for further crash tests.
To allow acceleration forces to be investigated in accidents without having to destroy a whole vehicle for this purpose, so-called crash tests using a carriage are conducted, in which a carriage is accelerated to the desired speed, for example by a pre-stressed elastic cable. The carriage then collides with a deformable obstacle at this speed. However, with this kind of test, it is difficult to recreate deceleration curves from real crash tests.
It is therefore also known to simulate the deceleration of a real crash test by an acceleration of the test object. This means that the acceleration forces acting on the movable masses of the vehicle on collision with an obstacle are exerted directly via an acceleration of the crash-test carriage onto the test object. Real deceleration curves can thus be recreated substantially better.
In known methods, in order to conduct such tests, the carriage is accelerated by a thrust rod which is hydraulically moved out of a cylinder tube in accordance with a real deceleration curve. In order to recreate the real deceleration curve, the hydraulic pressure exerted on the thrust rod is controlled by a hydraulic valve. In view of the high degree of acceleration required, this thrust rod must be capable of being actuated at an extremely high rate and must be able to react very quickly. A plurality of calibration tests must be conducted for the adaptation to the real deceleration curve since such a valve cannot be regulated within the test time of a maximum of 100 milliseconds. This process is therefore relatively expensive and time-consuming.
The present invention provides a method for conducting crash tests using a carriage with which real deceleration curves can likewise be recreated very precisely, but which is less expensive and time-consuming, and includes an apparatus for carrying out such a method.
According to the present invention, during the test, a first force is exerted on the crash-test carriage in the direction of acceleration, this first force being larger than a respective second force required for acceleration in accordance with the real deceleration curve, on the one hand. In order to achieve the desired acceleration curve, a braking force opposite to the direction of acceleration is exerted on the crash-test carriage or on an apparatus driving it, this braking force being so large that the resulting force accelerates the carriage in accordance with the desired acceleration curve, on the other hand.
The generation of acceleration and the adaptation of the acceleration to a desired curve can be advantageously separated from one another by the exertion of an acceleration force on the crash-test slide, on the one hand, and of a braking force, on the other hand. The adaptation is thereby possible with a relatively low effort. In particular, a regulation can be carried out. Time-consuming calibration tests are thereby made superfluous so that the method overall requires much less effort than the one described with respect to the related art and, nevertheless, allows a very exact adaptation to the desired acceleration curve.
In accordance with an embodiment of the invention, the force acting in the direction of acceleration is produced pneumatically. It is possible to pneumatically generate a force in a simple manner and allows, likewise in a simple manner, a repeated conducting of crash tests using a carriage.
In accordance with a further embodiment of the invention, a pressure is generated in a pressure reservoir at a maximum braking force, the pressure corresponding at least to the maximum required acceleration force, and, subsequently, the brake is gradually opened in accordance with the acceleration curve. In this way, the adaptation of the acceleration to the acceleration curve can be achieved solely by a controlled or regulated opening of the brake. This adaptation is, in particular, of advantage when carrying out a real-time regulation.
In accordance with a further embodiment of the invention, the generation of the required pressure is controlled via a pressure sensor arranged in the pressure reservoir, in particular by using a computer. In this way, the exact pressure generation is ensured in the pressure reservoir.
In accordance with a further embodiment of the invention, the braking force is hydraulically transferred onto the brake carriage or onto an apparatus driving it. An exact control and regulation is thus possible in a particularly easy manner. As a result of the relatively low amount of hydraulic fluid required, valves with a comparatively low flow rate, in particular standard hydraulic valves, can be used, which can also be regulated in real time.
In accordance with a further embodiment of the invention, an emergency braking of an apparatus driving the crash-test carriage is carried out at the end of the crash test using a carriage, with the end of the crash test preferably being determined via the path covered, the time and/or the speed of the crash-test carriage. The exertion of an uncontrolled force on the crash-test carriage after the end of the test is thus prevented.
An apparatus for conducting the method includes, in accordance with the invention, a pressure chamber whose volume is restricted by a piston which acts on the crash-test carriage via a thrust rod; a compressor for generating the required pressure in the pressure chamber; and a braking device for acting on the crash-test carriage or on the thrust rod. Crash tests using a carriage in accordance with the invention can thus be conducted in an advantageous manner with pneumatic acceleration.
In accordance with a further embodiment of the invention, the pressure chamber has a safety valve to restrict the maximum pressure. Damage to the system due to excess pressure is thereby avoided.
In accordance with a further embodiment of the invention, a pressure sensor is present in the pressure chamber whose output signal is transmitted to a control unit to control the pressure generation. The achieving of the required pressure in the pressure chamber is thus ensured.
In accordance with a further embodiment of the invention, a pressure switch is provided in the pressure chamber whose response pressure lies somewhat below the safety valve pressure. Upon reaching the response pressure, the pressure switch switches off the compressor. The compressor is thus automatically switched off before the maximum permitted pressure is reached, and the occurrence of excess pressure is avoided.
In accordance with a further embodiment of the invention, the brake device acting on the crash-test carriage or on the thrust rod can be hydraulically actuated. This hydraulic actuation is advantageous for construction and allows a control, and in particular a regulation, of the braking force. A standard hydraulic valve is preferably provided for this purpose.
In accordance with a further embodiment of the invention, the braking force can be regulated dependent on the acceleration of the crash-test carriage. An acceleration sensor is provided therefor which measures the acceleration of the crash-test carriage. Another possibility includes regulating the braking force dependent on the desired pressure of the hydraulic brake.
In accordance with a further embodiment of the invention, the crash-test carriage can be displaced by a thrust rod, the thrust rod engaging loosely at the carriage, with the brake device preferably acting on the thrust rod. This set-up is advantageous for construction and also allows the crash-test carriage to roll out at the end of the test.
In accordance with a further embodiment of the invention, a plurality of units are provided in order to generate the acceleration force. The force required to accelerate the crash-test carriage can thereby be generated more simply.